1. Field of the Invention
The present invention relates to an automatic document feeder for conveying consecutively document sheets to a document reading position, said automatic document feeder being used in an image reader for forming an image on a paper sheet such as an electrophotographic copying machine for example.
2. Prior Art
An image reader of an electrophotographic copying machine and the like as described above uses a document sheet conveying device called an automatic document feeder (ADF) so as to automatically draw out and feed one by one a plurality of document sheets to a document reading position.
As disclosed in Japanese Patent Laid-Open Publication No. Hei 8-133,551 for example, such a document sheet conveying mechanism is formed so as to draw out one by one document sheets stacked on a paper feed stacker by means of a document sheet separating mechanism, convey each of them to an information reading position through a paper feed path and, after a document sheet is scanned in order to optically take an image on the document sheet, discharge the scanned document sheet onto a paper discharge stacker through a paper discharge path and a pair of paper discharge rollers arranged in the paper discharge path.
In this case, a paper feed roller for drawing out a document sheet, a pair of conveying rollers for conveying a document sheet drawn out and a pair of discharge rollers are driven by a plurality of driving motors.
On the other hand, an image reader is provided with a scanning means for reading each of document sheets one by one conveyed to a document reading position by an automatic document feeder. This scanning means includes a means of irradiating a document sheet passing on a platen with light, collecting the reflected light by means of a collective lens and detecting it by means of a CCD linear sensor, a means of irradiating a document sheet passing on a platen with light and detecting directly the reflected light by means of a contact sensor without collecting the reflected light, and the like.
By the way, in case of scanning a document sheet being conveyed by means of such a scanning means, there is a problem that a read image is distorted when the document sheet flaps at an actual reading position. As disclosed in Japanese Patent Laid-Open Publication No. Hei 10-139,211 for example, therefore, there is known a technique for smoothly feeding a document sheet into a gap (a document reading position) between a platen and a sheet holding member.
That is to say, this publicly known technique arranges a pair of upper and lower plate-shaped elastic pieces at the upstream side of a document reading position, guides a document sheet as putting it between these elastic pieces and thereby feeds the document sheet to the document reading position on a stable track without varying its attitude.
However a general automatic document feeder is provided with a guide for picking up the fore end of a read document sheet and guiding it to a paper discharge slacker side (hereinafter referred to as a xe2x80x9cpickup guidexe2x80x9d), and has a conveying path being bent (curved) from the reading position toward the paper discharge side.
Due to this, the publicly known technique described above has a problem that a document sheet can be fed smoothly to a reading position but since a document sheet passing the reading position moves through a path being bent (curved) at a pickup guide position, when the fore end of the document sheet strikes this curved part the document sheet flaps at the reading position. Therefore, this technique cannot surely prevent the distortion of a read image and brings a result of obtaining a read image being large in distortion, particularly in case of using a contact sensor as a scanning means.
On the other hand, in a general automatic document feeder, since various rollers are driven by a plurality of driving motors when a document sheet is conveyed, a driving system is complicated and the apparatus is made large-sized and therefore the speed of a reading process becomes slow.
And since a document sheet is discharged by a paper discharge path and a pair of paper discharge rollers arranged in this path, the apparatus is necessarily made large-sized, and thereby in case of consecutively reading document sheets the speed of the reading process is made slower.
Further, since a document sheet is discharged onto a paper discharge stacker through a pair of paper discharge rollers, the state of discharged sheets is not made stable in the direction of discharge and the paper discharge stacker is made large-sized in this direction or a large-sized document sheet is projected from the paper discharge stacker.
The present invention has been performed paying attention to the above problems, and an object of the present invention is to provide an automatic document feeder capable of making the whole apparatus small-sized, simplifying its driving system, improving the speed of reading consecutive document sheets and discharging the document sheets stably onto a paper discharge stacker.
Further, another object of the invention is to provide an automatic document feeder capable of surely preventing an image read in an image reader from being distorted when conveying a document sheet to a document reading position of the image reader.
In consideration of the above-mentioned problems of the prior art, an automatic document feeder according to the present invention is an automatic document feeder which has a conveying roller for conveying a document sheet, conveys a document sheet to a document reading position on a platen facing a document image reading portion with said document sheet between them and comprises a pickup guide for picking up the fore end of a document sheet scanned at said document reading position from said platen and a pressing piece for pressing a document sheet being conveyed against said pickup guide at a curved part provided by said platen and said pickup guide.
Hereupon, said pressing piece is fixed at the upstream side of said document reading position, extends from said fixed position across the document reading position and is made free at the downstream side. Or the upstream end portion of said pressing piece may be fixed at said document reading position and the downstream end portion of it may extend from the said fixed position across the document reading position and be free in a hanging state.
Said pressing piece is made of a white Mylar member and is made wider in width than the largest document sheet to be conveyed in consideration of handling a thin document sheet.
Further, it is provided with an elastic member so as to make said Mylar member parallel with said curved portion in order to more surely make the document surface of a document sheet close to the document reading portion. As said elastic member, a sponge material or a spring material is used, for example.
Said pressing piece is detachably attached to a frame forming an automatic document feeder or a module guide forming a document sheet conveying path in conjunction with said conveying roller, so that said pressing piece is easily cleaned or maintained. For this purpose, a double-faced adhesive tape is adhered to one end portion of the pressing piece.
According to such a composition as described above, even if a document sheet passing the document reading position is conveyed so as to be curved at a pickup guide provided at the downstream side of the document reading position, since the document sheet is always pressed by the pressing piece, the document sheet does not flap at the document reading position and is not jammed, and an image on the document sheet can be read accurately.
Furthermore, the present invention is to provide an automatic document feeder which has a conveying roller for conveying a document sheet, conveys a document sheet to a document reading position on a platen facing a document image reading portion with said document sheet between them, comprising a pickup guide for picking up the fore end of a document sheet scanned at said document reading position from said platen, a paper discharge means for discharging a document sheet passing said platen onto a paper discharge tray, and a curved path where said document reading portion for reading a conveyed document sheet is located, wherein, said paper discharge means discharges a document sheet onto the paper discharge stacker and a document sheet deflecting means for deflecting a document sheet toward the paper discharge stacker is provided.
And said paper discharge means has a paper discharge roller and said document sheet deflecting means is formed out of a plate spring being swayable. The end portion of said plate spring in the paper discharge direction is curved following the circumferential face of said paper discharge roller. Said plate spring is arranged so that the fore end of a conveyed document sheet strikes it at an acute angle and guides the fore end of a conveyed document sheet in a state where the fore end of the conveyed document sheet is in contact with said plate spring at an acute angle to the nipping part of the paper discharge roller. Said paper discharge roller is supported so that the outer circumferential face of it projects from the rear end stop plate of said paper discharge stacker.
An image reader of the present invention comprises a paper feed stacker and a paper discharge stacker provided at upper and lower positions relative to each other, a curved path which is arranged between these paper feed stacker and paper discharge stacker and through which a document sheet is conveyed, a paper feed means formed in a path for conveying a document sheet, a conveying means, a paper discharge means, and a driving motor for driving these document sheet conveying means, and feeds a document sheet conveyed by said conveying means to a document sheet reading portion, discharges a document sheet read by said document sheet reading portion onto said paper discharge stacker by means of said document sheet discharge means and comprises a document sheet deflecting means for deflecting a document sheet toward the paper discharge stacker.
Said paper feed means provided in said image reader is provided with a resisting roller for removing the skew of a document sheet fed from said paper feed stacker, said conveying means is provided with a feed roller for feeding a document sheet whose skew has been removed to a document sheet reading portion, and said paper discharge means is provided with a paper discharge roller for discharging a document sheet read by the document sheet reading portion onto the paper discharge stacker.
And said resisting roller, feed roller and paper discharge roller are in contact with the outer circumferential face of a single large-diameter roller.
Such a composition as described above makes it possible to drive and control a paper feed means, a conveying means and a paper discharge means in conveyance of a document sheet by means of a single driving motor and thereby simplify the driving system and control system. And since a document sheet read by a document sheet reading portion is discharged in a state of being deflected by a deflecting means, the paper discharge state is made stable.